Method for manufacturing a sensor bearing unit

ABSTRACT

The method provides for the manufacturing a sensor bearing unit including a bearing having a first ring and a second ring capable of rotating concentrically relative to one another, and an impulse ring provided with a target holder secured to the first ring and with a magnetic target mounted on the target holder. The method further includes securing the target holder to the first ring, and magnetizing the magnetic material of the magnetic target after the step of securing the target holder to the first ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application no.102020206479.2, filed May 25, 2020, the contents of which is fullyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a sensorbearing unit. More precisely, the present invention relates to a methodfor manufacturing a sensor bearing unit comprising a bearing and animpulse magnetic ring.

BACKGROUND OF THE INVENTION

Today, sensor bearing units are commonly used in a wide range oftechnical fields, for example in automotive industry and aeronautics.These units provide high quality signals and transmissions, whileallowing integration in simpler and more compact apparatus.

Such a sensor bearing unit generally comprises a bearing, an impulsering, and detection means facing the impulse ring. For example, theimpulse ring is provided with a target holder fixed to the inner ring ofthe bearing, and with a magnetized target fixed to the target holderbeyond the outer ring of the bearing.

The magnetic target includes alternating North and South poles, whosenumber depends on bearing size, detection precision and particularapplication. The detection means may be fixed to the outer ring of thebearing or to a fixed casing.

The magnetic target is attached to an outer tubular portion of thetarget holder. The target holder is also provided with an inner tubularportion secured into a groove made in the bore of the inner ring.

Classically, this groove of the inner ring is soft turned, and then aheat treatment is applied on the inner ring. Then, the magnetic poles ofthe target ring are created by magnetization. After that, the targetholder provided with the target ring is secured into the groove of theinner ring.

With this sequence of operations, the groove presents a largeconcentricity defect with the inner ring bore diameter. This defectcauses a degradation of the total pitch deviation of the magnetic targetduring assembly of the impulse ring with the inner ring.

The total pitch deviation, named TPD, is a parameter used tocharacterized the magnetic ring. It evaluates the cumulative error onthe position of the magnetic ring by measuring the single pitchdeviation for each ring pole.

Determination of the TPD for a magnetic ring with magnetic poles issimilar to the determination of the TPD for gears or mechanical encodersas seen in ABS applications.

An interval is defined as the angular distance between two nearest polesof same polarity. A general method to calculate TPD is described by thefollowing equations:

Single pitch deviation error SPD for interval i can be calculated on thebasis of the formula:

${{SPD}(i)} = {\frac{P_{Theoretical} - {P_{real}(i)}}{P_{Theoretical}} \times 100}$

wherein:

P_(Theoretical): Theoretical period of the angular signal for aninterval

P_(real)(i): Actual period of the angular signal for interval i.

It is to be noted that the actual period P_(real)(i) is to be determinedbetween poles of same sign, i.e. between North poles or between Southpoles. Similarly, the actual period P_(real)(i) is to be determinedbetween the same kind of signal edges, i.e. between rising edges orbetween falling edges.

Total or cumulative pitch deviation error TPD(i) for interval i can becalculated on the basis of the formula:

${{TPD}(i)} = {\sum\limits_{n = 1}^{n = i}{{SPD}(n)}}$

Total pitch deviation error TPD on a mechanical turn can be calculatedon the basis of the formula:

${TPD} = {{\max\left( {\sum\limits_{i = 1}^{1 = {Nbpp}}{{SPD}(i)}} \right)} - {\min\left( {\sum\limits_{i = 1}^{i = {Nbpp}}{{SPD}(i)}} \right)}}$

wherein Nbpp: Number of intervals in a mechanical turn.

One aim of the present invention is to overcome the above-mentioneddrawback.

SUMMARY OF THE INVENTION

The invention relates to a method for manufacturing a sensor bearingunit comprising a bearing comprising a first ring and a second ringcapable of rotating concentrically relative to one another, and animpulse ring provided with a target holder secured to the first ring andwith a magnetic target mounted on the target holder.

The method comprises the following steps:

-   -   a) securing the target holder to the first ring, and    -   b) magnetizing the magnetic material of the magnetic target        after the step of securing the target holder to the first ring.

Such a manufacturing method limits the degradation of the total pitchdeviation value of the magnetic target installed onto the associatedring. The measurement accuracy of the sensor bearing unit is improved.

According to further aspect, at step b) the magnetic material of themagnetic target is magnetized in order to create North and Southalternated poles.

Preferably, at step a) the target holder is secured inside a groove madein a cylindrical surface of the first ring.

At step b) a magnetization yoke may be centered directly on thecylindrical surface of the first ring having the groove.

In one embodiment, at step a) the target holder is secured inside thegroove which is formed in the bore of the first ring.

In another embodiment, at step a) the target holder is secured insidethe groove which is formed in the outer cylindrical surface of the firstring.

The method may further comprise, before step a), the step of machiningthe groove in the cylindrical surface of the first ring.

According to further aspect, the method may further comprise assemblingthe components of the bearing before step b). This assembly step may bedone after step a) or before step a).

Alternatively, the components of the bearing may be assembled after stepb).

The invention relates to a method for manufacturing a sensor ring for asensor bearing unit, the sensor ring comprising a ring and an impulsering provided with a target holder secured to the ring and with amagnetic target mounted on the target holder.

The method comprises the following steps:

-   -   a) securing the target holder to the ring, and    -   b) magnetizing the magnetic material of the magnetic target        after the step of securing the target holder to the ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be better understood bystudying the detailed description of specific embodiments given by wayof a non-limiting examples and illustrated by the appended drawings onwhich:

FIG. 1 is an axial section view of a sensor bearing unit according to anexample of the invention,

FIG. 2 shows the main steps of a method for manufacturing the sensorbearing unit of FIG. 1 according to a first example of the invention,

FIGS. 3 and 4 are curves showing the evolution of the total pitchdeviation of a magnetic impulse ring for the sensor bearing unit of FIG.1 and for a conventional sensor bearing unit, and

FIG. 5 shows the main steps of a method for manufacturing the sensorbearing unit of FIG. 1 according to a second example of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The sensor bearing unit 10 represented on FIG. 1 is adapted to equip anapparatus such a motor, a brake system, a suspension system or anyrotating machine, in particular for an automotive vehicle.

The sensor bearing unit 10 comprises a bearing 12 and an impulse ring 14mounted on the bearing.

The bearing 12 comprises comprising a first ring 16 and a second ring18. In the illustrated example, the first ring 16 is the inner ringwhereas the second ring 18 is the outer ring. The inner and outer rings16, 18 are concentric and extend axially along the bearing rotation axisX-X′ which runs in an axial direction. The inner and outer rings 16, 18are made of steel.

In the illustrated example, the bearing 12 also comprises a row ofrolling elements 20, which are provided here in the form of balls,interposed between raceways (not referenced) formed on the inner andouter rings 16, 18. The rolling bearing 10 also comprises a cage 22 formaintaining the regular circumferential spacing of the rolling elements20.

The inner ring 16 of the bearing is intended to be mounted on a shaft ofthe apparatus for tracking the rotation of the shaft. The inner ring 16is intended to rotate while the outer ring 18 is intended to be fixed.The outer ring 18 can be mounted in a fixed support member or housing,belonging to the apparatus.

The inner ring 16 comprises a cylindrical inner surface or bore 16 a andan outer cylindrical surface 16 b which is radially opposite to the bore16 a and from which a toroidal circular raceway for the rolling elements20 is formed, said raceway being directed radially outwards. The innerring 16 further comprises two opposite radial lateral faces 16 c, 16 dwhich axially delimit the bore 16 a and the outer surface 16 b of saidring.

The inner ring 16 also comprises a cylindrical groove 16 e made in thebore 16 a. The groove 16 e is centered on the axis X-X′. Diameter ofbore 16 a is smaller than diameter of groove 16 e. The groove 16 e openson the radial lateral face 16 d.

The impulse ring 14 is mounted on the inner ring 16. The impulse ring 14comprises an annular target holder 30 mounted on the inner ring 16, anda magnetic target 32 mounted on said target holder.

The target holder 30 is secured into the annular groove 16 e of theinner ring. The target holder 30 comprises an inner annular axialportion 30 a mounted into the groove 16 e, an outer annular axialportion 30 b radially surrounding the inner axial portion 30 a and thebearing 12, and an annular radial portion 30 c extending between saidinner and outer axial portions.

The inner axial portion 30 a of the target holder is secured into thegroove 16 e of the inner ring to fasten in rotation the impulse ring 14with the rotatable inner ring 16. For example, the inner axial portion30 a of the target holder may secured into the groove 16 e, bypress-fitting, by snapping, by gluing, by welding or any otherappropriate means.

In the disclosed example, the radial portion 30 c of the target holderaxially comes into contact against the radial lateral face 16 d of theinner ring. The outer axial portion 30 b of the target holder is locatedradially above the outer ring 18 of the bearing.

In the disclosed example, the target holder 30 is made in one part. Thetarget holder 30 may be made of metal or plastic, formed by stamping orby any other suitable process.

The magnetic target 32 is mounted on the outer axial portion 30 b of thetarget holder. In the disclosed example, the magnetic target 32 ismounted into the bore of the outer axial portion 30 b. Alternatively,the magnetic target 32 may be mounted on the outer surface of the outeraxial portion 30 b.

The magnetic target 32 includes magnetic North and South alternatedpoles. The magnetic target 32 is multi-polarly magnetized in thecircumferentially direction. The magnetic target 32 may be a plasticmolded part. The magnetic target 32 may be overmolded onto the targetholder 30. Alternatively, the magnetic target 32 may be separatelyformed and secured onto the target holder 30 by any appropriate means,for example by bonding or by press-fitting. The magnetic target 32 maybe formed of a rubber material with magnetic powder, or of a magneticalloy or of a plasto-ferrite or of an elasto-ferrite.

Detection means (not shown) are associated with the target 32 fortracking the rotation of the impulse ring 14 and the inner ring 16around the axis X-X′. The detection means are disposed to radially facethe inner surface of the magnetic target 32. For example, the detectionmeans may include Hall-effect sensors.

FIG. 2 shows the main steps of a method for manufacturing the sensorbearing unit 10 according to an example of the invention.

According to this example, the manufacturing method provides an assemblystep 40 of the components of the bearing 12, namely the inner and outerrings 16, 18, the rolling elements 20 and the cage 22. The groove 16 eof the inner ring may be machined, for example by turning, after orbefore the assembly step 40.

After the assembly step 40, the target holder 30 provided with thetarget ring 32 is mounted on the inner ring 16 during a step 42. Duringthis mounting step 42 of the target holder, the inner axial portion 30 aof the target holder is introduced into the groove 16 e of the innerring. Optionally, the target holder 30 may be turned in thecircumferential direction inside the groove 16 e of the inner ring to aspecific angular position. Then, the target holder 30 is secured insidethe groove 16 e of the inner ring.

Otherwise, in this example, the target ring 32 is mounted on the targetholder 30 before the mounting step 42 of the target holder on the innerring. Alternatively, the target ring 32 may be mounted on the targetholder 30 after the mounting step 42.

In this example, the manufacturing method begins with the assembly step40 of the components of the bearing 12. Alternatively, the manufacturingmethod may begin with the mounting step 42 of the target holder 30 onthe inner ring 16, for example if the bearing 12 is assembled on adifferent production site that is remote from the site where the targetholder 30 is mounted on the inner ring 16.

Then, a magnetization step 44 is achieved on the target ring 32. Themagnetization step 44 is achieved to create North and South alternatedpoles. During this step 44, a magnetization yoke is used and may becentered directly on the inner ring bore 16.

The magnetization yoke may have a pair of tooth profiles having anexciting coil wound thereon. In a first sub-step, the tooth profiles areclosely radially arranged on the bore of the target ring 32. In thisstate, a current is fed to the exciting coil for generating a magneticflux in the radial direction so that said magnetic flux passes throughthe target ring 32 for obtaining a pair of North and South poles.Thereafter, a second sub-step of rotating the target ring 32 togetherwith the target holder 30 by a prescribed angle and magnetizing the sameis repeated thereby multi-polarly magnetizing the overall bore of thetarget ring 32 in the circumferential direction. The North and Southalternated poles exhibit substantially identical magnetization strength.

With the manufacturing method of the invention having the magnetizationstep of the magnetic target 32 done after installation of the targetholder 30 on the inner ring 16, the degradation of the total pitchdeviation of the target ring 32 is limited.

On FIG. 3, the curve 50 shows the evolution of the total pitch deviationof the magnetic target 32 (FIG. 1) of the impulse ring for the sensorbearing unit manufactured according to the invention, the total pitchdeviation being measured at various radial airgaps between the Halleffect cell and the magnetic target 32.

The curve 52 shows the evolution of the total pitch deviation of themagnetic target of an impulse ring of a conventional sensor bearing unithaving the magnetization step of the magnetic target done beforeinstallation of the target holder on the inner ring, the total pitchdeviation being also measured at various radial airgaps between the Halleffect cell and the magnetic target.

As shown on FIG. 3, for the sensor bearing unit manufactured accordingto the invention, the values of the total pitch deviation are limited.

On FIG. 4, the curves 54, 56 also respectively show the evolution of thetotal pitch deviation of the magnetic target of the impulse ring for thesensor bearing unit manufactured according to the invention, and for aconventional sensor bearing unit. Here, the total pitch deviation ismeasured at various axial reading positions between the Hall effect celland the magnetic target.

As shown on FIG. 4, the total pitch deviation of the impulse ring forthe sensor bearing unit manufactured according to the invention isalways smaller than for a conventional sensor bearing unit no matter theaxial position is.

FIG. 5 shows the main steps of a method for manufacturing the sensorbearing unit according to another example of the invention.

In this example, the manufacturing method provides a mounting step 60 ofthe target holder 30 on the inner ring 16 which is a stand-alone ring.The inner axial portion 30 a of the target holder is introduced into thegroove 16 e of the inner ring. Optionally, the target holder 30 may beturned in the circumferential direction inside the groove 16 e of theinner ring to a specific angular position. Then, the target holder 30 issecured inside the groove 16 e of the inner ring.

Preferably, the target holder 30 mounted on the inner ring 16 isequipped with the target ring 32. Alternatively, the target ring 32 maybe mounted on the target holder 30 after the mounting step 60.

Then, the manufacturing method provides a magnetization step 62. Themagnetization step 62 is performed as previously described in the firstexample.

The manufacturing method further comprises an assembly step 64 of thecomponents of the bearing 12, namely the inner and outer rings 16, 18,the rolling elements 20 and the cage 22.

In this example, the manufacturing method ends with the assembly step 64of the components of the bearing 12. Alternatively, the magnetizationstep 62 and the assembly step 64 may be inverted.

In the illustrated examples, the sensor bearing unit is provided with arolling bearing comprising one row of rolling elements. Alternatively,the rolling bearing may comprise at least two rows of rolling elements.In the illustrated examples, the rolling elements are balls.Alternatively, the rolling bearing may comprise other types of rollingelements, for example rollers. In another variant, the rolling bearingmay also be provided with a sliding bearing having no rolling elements.

Otherwise, as previously mentioned, in these illustrated examples, thefirst ring of the rolling bearing is the inner ring 16 whereas thesecond ring is the outer ring 18. As an alternative, it could bepossible to provide a reversed arrangement with the first ring formingthe outer ring and the second ring forming the inner ring. In this case,the target holder is secured to the outer ring.

In the illustrated examples, the method relates to the manufacturing ofthe sensor bearing unit.

The invention also relates to a method for manufacturing a sensor ringfor the sensor bearing unit, the sensor ring being the inner or outerring equipped with the impulse ring. If the sensor ring is the innerring, the manufacturing method differs from the one as previouslydescribed in the second example only in the fact said method does notcomprise the assembly step 64 of the components of the bearing. As amatter of fact, in this case, the bearing with the sensor ring isassembled on a different production site that is remote from the sitewhere the target holder 30 is secured to the inner ring and where thetarget ring 32 is then magnetized.

1. A method for manufacturing a sensor bearing unit comprising:providing a bearing comprising a first ring and a second ring capable ofrotating concentrically relative to one another, and an impulse ringincluding a target holder secured to the first ring and with a magnetictarget mounted on the target holder, wherein the method comprises thefollowing steps: a) securing the target holder to the first ring, and b)magnetizing the magnetic material of the magnetic target after the stepof securing the target holder to the first ring.
 2. The method accordingto claim 1, wherein at step b) the magnetic material of the magnetictarget is magnetized in order to create North and South alternatingpoles.
 3. The method according to claim 1, wherein at step a) the targetholder is secured inside a groove made in a cylindrical surface of thefirst ring.
 4. The method according to claim 3, wherein at step b) amagnetization yoke is centered directly on the cylindrical surface ofthe first ring having the groove.
 5. The method according to claim 3,wherein at step a) the target holder is secured inside the groove whichis formed in the bore of the first ring.
 6. The method according toclaim, wherein at step a) the target holder is secured inside the groovewhich is formed in the outer cylindrical surface of the first ring. 7.The method according to claim 3, further comprising, before step a), thestep of machining the groove in the cylindrical surface of the firstring.
 8. The method according to claim 1, further comprising assemblingthe components of the bearing before step b).
 9. The method according toclaim 1, further comprising assembling the components of the bearingafter step b).
 10. A method for manufacturing a sensor ring for a sensorbearing unit, comprising: providing the sensor ring comprising a ringand an impulse ring provided with a target holder secured to the ringand with a magnetic target mounted on the target holder, the methodcomprises the following steps: a) securing the target holder to thering, and b) magnetizing the magnetic material of the magnetic targetafter the step of securing the target holder to the ring.